HARQ in Spatial Multiplexing MIMO System

ABSTRACT

A method and apparatus for signaling scheduling information in a spatial multiplexing wireless communications system, as well as corresponding methods and apparatus for processing such signaling information, are disclosed. Signaling scheduling information includes scheduling first and second transport blocks for simultaneous transmission during a first transmission interval on first and second data substreams, respectively, and assigning a single re-transmission process identifier for the first transmission interval and transmitting first scheduling information for the first transmission interval. The first scheduling information includes the re-transmission process identifier and first disambiguation data. Additionally, at least one of the first and second transport blocks is scheduled for re-transmission during a second transmission interval. Second scheduling information for the second transmission interval is also transmitted; the second scheduling information including the re-transmission process identifier and second disambiguation data.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/246,530, filed on Sep. 27, 2011, which is a continuation of U.S.patent application Ser. No. 12/447,522, which is the National Stage ofInternational Application PCT/SE2007/050782 filed Oct. 26, 2007, whichclaims the benefit of priority from foreign application SE 0602300-6filed Oct. 31, 2006. The contents of each of the '530, '522, '782, and'300-6 applications are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates generally to wireless communicationssystems, and more particularly to the signaling of schedulinginformation in a spatial multiplexing wireless communications systemutilizing re-transmissions for error control.

BACKGROUND

Over the last few decades, a wide variety of both wired and wirelesstelecommunication systems have been developed. Wirelesstelecommunication systems in particular have evolved through theso-called second generation (2G) systems into the third generation (3G)systems currently being deployed. Specifications for some 3G systemswere developed by the 3rd Generation Partnership Project (3GPP);information regarding these may be found on the Internet atwww.3gpp.org.

Continuing development of advanced wireless systems has producedtechniques enabling even higher data transfer speeds. To this end,so-called High-Speed Downlink Packet Access (HSDPA) technology hasrecently been developed. HSDPA delivers packet data to a plurality ofmobile terminals over a shared downlink channel at high peak data rates,and provides a smooth evolutionary path for 3G networks to supporthigher data transfer speeds.

HSDPA achieves increased data transfer speeds by defining a new downlinktransport channel, the High-Speed Downlink Shared Channel (HS-DSCH),which operates in significantly different ways from other W-CDMAchannels. In particular, the HS-DSCH downlink channel is shared betweenusers, and relies on user-specific channel-dependent scheduling to makethe best use of available radio resources. On a separate uplink controlchannel, each user device periodically transmits (e.g. as many as 500times per second) an indication of the downlink signal quality. TheWideband-CDMA base station (Node B) analyzes the channel qualityinformation received from all user devices to decide which users will besent data on each 2-millisecond frame and, for each user, how much datashould be sent in that frame. Using adaptive modulation and coding (AMC)techniques in addition to this frame-by-frame fast packet scheduling,more data can be sent to users which report high downlink signalquality. Thus, the limited radio resources are used more efficiently.

To support the newly defined HS-DSCH channel, three new physicalchannels are also introduced. First is the High-Speed Shared ControlChannel (HS-SCCH), which is used to convey scheduling information to theuser device. In essence, this scheduling information describes data thatwill be sent on the HS-DSCH two slots later. Second is the uplinkHigh-Speed Dedicated Physical Control Channel (HS-DPCCH), which carriesacknowledgement information transmitted by mobile terminals as well ascurrent channel quality indicator (CQI) data for the user device. TheCQI data is used by the Node B in its fast packet scheduling algorithms,i.e., in calculating how much data to send to the mobile terminal duringthe next transmission interval. Finally, a newly defined downlinkphysical channel is the High-Speed Physical Dedicated Shared Channel(HS-PDSCH), which is the physical channel carrying the user data of theHS-DSCH transport channel.

In addition to the fast packet scheduling and adaptive modulation andcoding technologies discussed above, HSDPA further utilizes fastretransmissions for error control. In particular, HSDPA utilizes anerror control method known as Hybrid Automatic Repeat Request, or HARQ.HARQ uses the concept of “incremental redundancy”, where retransmissionscontain different coding of the user data relative to the originaltransmission. When a corrupted packet is received, the user device savesit, sends a “NACK” message to trigger a re-transmission of the packet,and combines the saved packet with subsequent retransmissions toformulate an error-free packet as quickly and efficiently as possible.Even if the retransmitted packet(s) is itself corrupted, the combiningof information from two or more corrupted transmissions can often yieldan error-free version of the originally transmitted packet.

In fact, HARQ is a variation of Automatic Repeat-reQuest (ARQ) errorcontrol, which is a well-known error control method for datatransmission in which the receiver detects transmission errors in amessage and automatically requests a retransmission from thetransmitter. HARQ gives better performance than ordinary ARQ,particularly over wireless channels, at the cost of increasedimplementation complexity.

The simplest version of HARQ, Type I HARQ, simply combines Forward ErrorCorrection (FEC) and ARQ by encoding the data block plus error-detectioninformation—such as Cyclic Redundancy Check (CRC)—with anerror-correction code (such as Reed-Solomon code or Turbo code) prior totransmission. When the coded data block is received, the receiver firstdecodes the error-correction code. If the channel quality is goodenough, all transmission errors should be correctable, and the receivercan obtain the correct data block. If the channel quality is poor andnot all transmission errors can be corrected, the receiver will detectthis situation using the error-detection code. In this case, thereceived coded data block is discarded and a retransmission is requestedby the receiver, similar to ARQ.

In more advanced methods, incorrectly received coded data blocks arestored at the receiver rather than discarded, and when the retransmittedcoded data block is received, the information from both coded datablocks are combined. When the transmitted and re-transmitted blocks arecoded identically, so-called Chase combining may be used to benefit fromtime diversity. To further improve performance, incremental redundancyHARQ has also been proposed. In this scheme, retransmissions of a givenblock are coded differently from the original transmission, thus givingbetter performance after combining since the block is effectively codedacross two or more transmissions. HSDPA in particular utilizesincremental redundancy HARQ, wherein the data block is first coded witha punctured Turbo code. During each re-transmission the coded block ispunctured differently, so that different coded bits are sent each time.

ARQ schemes in general may be utilized in stop-and-wait mode (aftertransmitting a first packet, the next packet is not transmitted untilthe first packet is successfully decoded), or in selective repeat mode,in which the transmitter continues transmitting successive packets,selectively re-transmitting corrupted packets identified by the receiverby a sequence number. A stop-and-wait system is simpler to implement,but waiting for the receiver's acknowledgement reduces efficiency. Thus,in practice multiple stop-and-wait HARQ processes are often performed inparallel so that while one HARQ process is waiting for anacknowledgement one or more other processes can use the channel to sendadditional packets.

The first versions of HSDPA address up to 8 HARQ processes, numbered 0through 7. This number is specified to ensure that continuoustransmissions to one user may be supported. When a packet has beentransmitted from the Node B, the mobile terminal will respond (on theHS-DPCCH) with an ACK (acknowledge) or NACK (not-ACK) indication,depending on whether the packet decoded correctly or not. Because of theinherent delay in processing and signaling, several simultaneous HARQprocesses are required. The Node B transmitter thus is able to transmitseveral new packets before an ACK or NACK is received from a previouspacket.

HSDPA as specified in 3GPP release 7 and forward is designed to achieveimproved data rates of up to 28.8 Mbps. This is accomplished byintroducing advanced multi-antenna techniques, i.e. Multiple-InputMultiple-Output (MIMO) technology. In particular, spatial multiplexingis employed to divide the data into two transmission streams, oftencalled data substreams. These substreams are transmitted with multipletransmit antennas, using the same frequencies and the samechannelization codes. Given uncorrelated propagation channels, receiversemploying multiple receive antennas and using advanced detectiontechniques such as successive interference cancellation are able todistinguish between and decode the multiplexed data substreams.

With the addition of MIMO to HSDPA, the number of required HARQprocesses increases, e.g. from 8 to 16 (0-15) processes. If theprocesses are independently numbered for each data substream andsignaled to the receiving mobile terminals, the signaling load on theHS-SCCH will increase significantly. Instead of a 3-bit HARQ processnumber for identifying eight processes, a 4-bit HARQ process number isneeded to distinguish between up to 16 processes. In a dual stream case,as currently under development for HSDPA systems, the signaling overheadwould thus increase from three to eight bits (two streams at fourbits/stream). Because signaling on HS-SCCH is relatively expensive,i.e., signaling bits are scarce, this increase in overhead isundesirable.

SUMMARY

The present invention provides methods and apparatus for signalingscheduling information in a spatial multiplexing wireless communicationssystem, as well as corresponding methods and apparatus for processingsuch signaling information. The inventive techniques described hereinfacilitate efficient signaling of re-transmission process information,such as may be employed in a hybrid automatic repeat-request (HARQ)error control system.

An exemplary method for signaling scheduling information, such as mightbe implemented at a 3GPP W-CDMA Node B, comprises scheduling first andsecond transport blocks for simultaneous transmission during a firsttransmission interval on first and second data substreams, respectively.The first and second data substreams may correspond to primary andsecondary data substreams of a 3GPP HSDPA dual-stream transmission. Theexemplary method further comprises assigning a single re-transmissionprocess identifier for the first transmission interval and transmittingfirst scheduling information for the first transmission interval, thefirst scheduling information comprising the re-transmission processidentifier and first disambiguation data. The method further comprisesscheduling at least one of the first and second transport blocks forre-transmission during a second transmission interval and transmittingsecond scheduling information for the second transmission interval, thesecond scheduling information comprising the re-transmission processidentifier and second disambiguation data. The first and seconddisambiguation data indicate whether the re-transmission of there-transmitted transport block is scheduled for the first or second datasubstream and may be used by a receiver to determine the same.

An exemplary method for processing scheduling information in a spatialmultiplexing wireless communication system, such as might be implementedin a 3GPP-compliant mobile terminal, comprises receiving firstscheduling information for a first transmission interval, the firstscheduling information comprising a single re-transmission processidentifier and first disambiguation data and receiving first and secondtransport blocks transmitted during the first transmission interval. Themethod further comprises receiving second scheduling information for asecond transmission interval, the second scheduling informationcomprising the same re-transmission process identifier and seconddisambiguation data. Finally, the exemplary method comprises using thefirst and second disambiguation data to determine whether are-transmitted transport block is scheduled for re-transmission on thefirst data substream or the second data substream during the secondtransmission interval.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. Upon reading the following descriptionand viewing the attached drawings, the skilled practitioner willrecognize that the described embodiments are illustrative and notrestrictive, and that all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates dual-stream transmission of transport blocksaccording to one scheme for assigning re-transmission processidentifiers.

FIG. 2 illustrates dual-stream transmission of transport blocks and theassignment of re-transmission process identifiers according to one ormore embodiments of the invention.

FIG. 3 illustrates an exemplary method for signaling schedulinginformation in a spatial multiplexing wireless communications system.

FIG. 4 illustrates another exemplary method for signaling schedulinginformation in a spatial multiplexing wireless communications system.

FIG. 5 illustrates an exemplary method for processing schedulinginformation in a spatial multiplexing wireless communications system.

FIG. 6 illustrates another exemplary method for signaling schedulinginformation in a spatial multiplexing wireless communications system.

FIG. 7 illustrates one embodiment of a spatial multiplexing wirelesscommunications system.

DETAILED DESCRIPTION

The present invention will be described below with reference to thefigures. Although the following description is primarily addressed tothe application of the inventive techniques to a W-CDMA HSDPA system,those skilled in the art will appreciate that the methods and devicesdescribed herein may also be applied in other spatial multiplexingwireless communications systems, including other systems that may or maynot employ CDMA technology. For example, 3GPP's Long-Term Evolution(LTE) initiative is currently specifying advanced 4th-generationwireless systems expected to support extremely high data rates (up to100 Mbit/sec) using technologies such as Orthogonal Frequency DivisionMultiplexing (OFDM), adaptive modulation and coding, fast packetscheduling, HARQ, and MIMO. Those skilled in the art will appreciatethat the inventive methods and apparatus described herein may readily beapplied to LTE signaling, as well.

A primary difference between HARQ operation for MIMO and non-MIMO HSDPAis the fact that two parallel processes can be transmitted indual-stream mode. Another difference is that a larger number ofre-transmission process identifiers need to be addressed even if only asingle transport block is transmitted. This is due to the rankadaptation that is present in the MIMO mode. Thus, when onlysingle-stream transmission is used, the HS-SCCH needs to be able tosignal any of the available HARQ processes, because an initialtransmission might occur during dual-stream mode, followed by are-transmission in single-stream mode. Accordingly, four HARQ processidentifier bits are required in the single-stream format of the HS-SCCH.

For the dual-stream case, several approaches have been proposed. Forcomplete flexibility, four bits per substream (in total eight bits) areneeded for re-transmission process identification. It should be notedthat if the quality of the two streams is varying over time, then theinitial transmission of a packet may be on one substream (e.g., theprimary substream, which has equal or higher-order modulation comparedto the secondary substream), while retransmission may occur on the other(e.g., the secondary substream). This might happen, for example, if anew transport block with higher modulation order is scheduled fortransmission during the same transmission interval as the re-transmittedtransport block 110 This is shown in FIG. 1, which illustrates adual-stream transmission scenario. Various transport blocks 110associated with re-transmission process identifiers RP-1 RP-2, etc., aretransmitted using a primary substream and a secondary substream. Thus,during a first transmission interval 115, transport blocks 110associated with RP-1 and RP-8 are transmitted. To signal thisscheduling, four re-transmission process identifier bits are sent on theHS-SCCH for each of the data substreams. In the example illustrated byFIG. 1, the transport block 110 associated with process identifier RP-1is not decoded correctly Thus a NACK 120 is sent to the Node B,indicating that this transport block 110 should be re-transmitted. At alater transmission interval 125, the incorrectly decoded transport block110 is rescheduled and transmitted using the secondary data substream,despite the fact that it was originally transmitted on the primarysubstream. However, because independent process identifier informationis sent for each substream in the scheduling message corresponding tointerval 125, the receiver is able to correctly match the re-transmittedtransport block 110 to the original failed transmission. Data from there-transmission may be combined with the originally received data toimprove the probability that the re-transmitted transport block 110 isdecoded correctly using incremental redundancy.

Although four bits per substream are required for maximum flexibility,fewer bits may be used if certain scheduling restrictions are accepted.For instance, one approach is to allocate a subset of the available HARQprocess identifiers to each substream. For example, re-transmissionprocess identifiers 0-7 could be associated with the primary substream,while identifiers 8-15 are used on the secondary. With this approach,only three bits for each substream might be used for signaling, thussaving two bits compared to the maximum-flexibility approach describedabove. On the other hand, this approach will impose some restrictions onthe scheduler. If a given transport block 110 is initially transmittedon the primary substream (with a process identifier of 0-7), it may notbe subsequently retransmitted on the secondary substream (processidentifiers 8-15). Thus, a significant restriction is imposed, for asavings of only two bits. For example, referring once more to FIG. 1, itis now impossible to retransmit process RP-1 on the secondary streamduring transmission interval 125, since this process “belongs” to theprimary stream.

An improved signaling scheme requires only three re-transmissionidentifier bits on the HS-SCCH during dual stream transmission. In thisapproach, the total number of process identifiers are grouped into pairs(e.g, {0A,0B}, {7A,7B}). A single process identifier is then associatedwith both substreams during a given transmission interval. The sub-pairs“A” and “B” are then coupled to the primary and secondary substreams,respectively. With this approach, only three bits per transmissioninterval are needed to signal a process identifier.

Although this approach yields reduced signaling, it also imposesrestrictions on the scheduler. However these tend to arise only duringspecial cases. An example of such a case is illustrated in FIG. 2. At afirst time interval 215, transport blocks 110 are transmitted on theprimary and secondary substreams and are associated with retransmissionprocess identifiers RP-1A and RP-1B. If both transport blocks 110 arereceived with uncorrectable errors, NACKs 120 will be sent for each, andthe Node B will attempt later to re-transmit both transport blocks 110.If channel conditions have changed in the meantime, only one stream maybe available for transmission, so that the transport blocks 110associated with process identifiers RP-1A and RP-1 B must be transmittedserially, as shown at transmission intervals 225 and 227. Thus, as shownat transmission interval 225, the transport block 110 for processidentifier RP-1A is transmitted on the primary substream, i.e., the onlyavailable stream for this interval. This is not in itself a problem, asfour bits are used for signaling the process identifier in single-streammode; the fourth bit may be used to distinguish between the “A”sub-process and the “B” sub-process. However, if channel conditionscontinue to change, such that both substreams are available for thesecond re-transmission interval 227, then channel capacity is wasted.Essentially, the capacity represented in FIG. 2 by transport block 230is not available for new data. This is because sub-process RP-1A isstill pending (since it was transmitted only one interval earlier) andcannot be re-used yet, since RP-1A must be coupled to RP-1B indual-stream mode. Accordingly, transmission of a new transport block 110(e.g., associated with process identifier RP-2A) must be delayed to thenext transmission time interval 235.

Those skilled in the art will recognize that this pairing scheme,although only requiring a total of three re-transmission processidentifier bits to be used during dual-stream mode, imposes certainadditional scheduling limitations, unless the scheme is slightlymodified. For example, if a given transport block 110 is initiallytransmitted on the primary substream, it cannot later be re-transmittedon the secondary substream, unless there is a signal to the receiver toindicate that the re-transmitted transport block 110 has “switched”substreams. As was discussed above, under certain circumstances it maybe desirable to permit scheduling re-transmissions on a differentsubstream. Thus, disambiguation data must also be signaled to thereceiver to resolve the potential ambiguity that arises whenre-transmitted transport blocks 110 may be scheduled on eithersubstream.

Fortunately, the basic scheme discussed above may be extended in atleast two ways to provide this disambiguation data. First, an additionalbit may be sent to indicate “orientation” of the sub-processes relativeto the substreams. For instance, a “0” value for this bit may indicatethat sub-process “A” is associated with the primary substream, whilesub-process “B” is associated with the secondary substream. A “1” valuewould indicate the opposite association, i.e. that sub-process “B” isassociated with the primary substream, and sub-process “A” with thesecondary. (Those skilled in the art will appreciate that theidentification of sub-processes is completely arbitrary; anyself-consistent sub-process identification scheme will suffice.) Withthis approach, a receiver that fails to decode a given transport block110 must save the process identifier (e.g., three bits for the exampleillustrated here) as well as this extra substream mapping bit. Thereceiver must also “remember” whether the failed transport block 110 wasreceived on the primary or secondary substream. When the NACKedtransport block 110 is re-transmitted (as indicated by there-transmission of the corresponding process identifier on the HS-SCCH),the receiver simply compares the current value of the substream mappingbit to the previous value. If the value is the same, then theretransmitted transport block 110 is scheduled for the same substream asbefore. If the value has changed, then the re-transmitted transportblock 110 is scheduled for the opposite substream.

An alternative way of describing this scheme is as follows. When twotransport blocks 110 are transmitted simultaneously, the relationshipbetween the transport blocks 110 and their respective re-transmissionprocess identifiers is such that when the transport block 110 associatedwith process identifier HARQ_ID is mapped to the primary substream, thenthe transport block 110 mapped to the secondary substream is associatedwith the re-transmission process identifier:(HARQ_ID+N_(HARQ)/2)mod(N_(HARQ)), where N_(HARQ) is the total number ofHARQ processes. Thus, where 16 total HARQ processes are supported,re-transmission process identifier “0” is linked with process identifier“8”, process identifier “1” is linked with process identifier “9’ and soon. Likewise, process identifier “9” is linked with process identifier“1”, identifier “10” with identifier “2”, and identifier “15” withidentifier “7”.

Those skilled in the art will appreciate that only four bits need besignaled to uniquely identify the paired process identifiers. Thoseskilled in the art, upon further reflection, will also recognize thatthis is precisely the modified signaling scheme described earlier. Threeof the four bits needed to signal the HARQ ID values correspond directlyto the three bits described earlier that uniquely identify thesub-process pairs {0A,0B}, . . . , {7A,7B}. The fourth bit correspondsdirectly to the substream mapping bit described above, and describes theorientation of the sub-processes relative to the primary and secondarysubstreams.

An alternative approach for sending the disambiguation data, i.e.,signaling the sub-process-to-substream mapping, involves the use ofimplicit signaling. With this approach, an explicit substream mappingbit is not used. Rather, other signaling information that can beuniquely associated with the originally transmitted transport block 110as well as with its re-transmissions can be used to determine whetherthe re-transmitted block is scheduled on the same or opposite datasubstream, compared to its original transmission. By comparing thisother signaling information received at a retransmission interval withthe corresponding information received at the original transmissioninterval, any ambiguity resulting from the re-mapping of there-transmitted transport block 110 may be resolved.

In one embodiment of this approach, the transport block size associatedwith the transport block 110 is used to derive this implicit substreammapping data. Those skilled in the art will appreciate that transportblocks 110 having any of several different transport block sizes may betransmitted at any given transmission interval in an HSDPA system. Thisis principally because of the adaptive coding and modulation scheme usedto match the coding to the channel condition. Because the receiver can“remember” the transport block size from an initial transmission of atransport block 110, the transport block size can be used to distinguisha re-transmitted transport block 110 from a transport block 110transmitted along with the re-transmitted transport block, provided thatthe transport block 110 simultaneously transmitted on the othersubstream has a different transport block size.

Thus, using this implicit approach, only three signaling bits need besent (for the case of 16 HARQ processes grouped into 8 pairs ofsub-processes), with the substream mapping derived from the transportblock size information. Those skilled in the art will appreciate thatthe transport block size may be signaled explicitly, as part of thescheduling data sent to the mobile terminal over the downlink controlchannel, or may be derived from other data, such as transport formatdata, that describes the modulation and coding for the transmissioninterval. As mentioned above, this approach also requires that atransport block 110 transmitted simultaneously with a re-transmittedblock must have a different transport block size (from there-transmitted block), so that the transport block 110 that comprisesre-transmitted data can be identified. Furthermore, to provide for thesituation where both transport blocks 110 in a given transmissioninterval are unsuccessfully decoded (and where both are re-transmittedtogether in a later interval), it may be desirable to require that everypair of simultaneously transmitted transport blocks 110 have differenttransport block sizes. With the flexibility afforded by the adaptivecoding and modulation schemes, this may not be a particularly severerestriction under many system conditions and/or configurations.

FIG. 3 thus illustrates a method for signaling scheduling information ina spatial multiplexing wireless communications system. The processbegins with the scheduling of first and second transport blocks 110 forsimultaneous transmission in a first transmission interval on a primaryand secondary data substream, respectively. A single re-transmissionprocess identifier is assigned for that transmission interval. Thus, asingle re-transmission process identifier corresponds to both of thetransport blocks 110 scheduled for that interval. In the exemplary HSDPAsystem described herein, the retransmission process identifier maycomprise a 3-bit datum, supporting 8 unique process identifiers.

At block 330, scheduling information corresponding to the firsttransmission interval is sent to the receiver over the downlink controlchannel (e.g., the HSDPA HS-SCCH). This scheduling information includesthe re-transmission process identifier as well as disambiguation datafor use in tracking the mapping of transport blocks 110 to the primaryand secondary substreams. In the method illustrated in FIG. 3, thisdisambiguation data comprises a single substream mapping bit.

At block 340, a NACK is received for at least one of the first andsecond transport blocks 110 sent during the first interval. Thoseskilled in the art will appreciate that this NACK may be receivedseveral transmission time intervals after the first interval, due tosignal propagation and processing delays. In response to the NACK, theNode B must re-schedule the NACKed transport block 110 (or blocks) for asubsequent interval.

Under some circumstances, the NACKed transport block 110 will bescheduled for the same substream as was used for the originaltransmission. However, in other circumstances it may be desirable toswitch substreams for the re-transmission of the NACKed transport block110. Thus, at block 350, the primary or secondary substream is selectedfor re-transmission of the NACKed transport block, based, inter alia, onthe then-current channel conditions. Then, at block 360, the NACKedtransport block 110 is scheduled for re-transmission, on the selectedsubstream, during a second transmission interval.

Scheduling information for the second transmission interval is sent atblock 370. This scheduling information includes a re-transmissionprocess identifier that is identical to the identifier sent for thefirst transmission interval, thus signaling to the receiver that atleast one of the data substreams carries a re-transmitted transportblock 110. In addition, the scheduling information includesdisambiguation data, in this case a second substream mapping bit, whichmay be used by the receiver to determine which substream carries there-transmitted transport block 110.

Those skilled in the art will appreciate that the scheduling informationmay include other signaling data for use by the receiver, including, forexample, re-transmission version information for use in incrementalredundancy processing. The scheduling may also include transport formatdata, which may explicitly identify a transport block size for each ofthe data substreams, or may alternatively define the modulation andcoding schemes in such a manner that the receiver may derive thetransport block sizes.

As was demonstrated above, transport block size information may serve asdisambiguation data in place of an explicit substream mapping bit. Anexemplary method employing this approach is illustrated in FIG. 4.

At block 410, the transmitting node (e.g., a W-CDMA HSDPA Node B)ensures that first and second transport blocks 110 to be scheduled forsimultaneous transmission have different transport block sizes. In manycases, this will naturally be the case, but it might need to be forcedin others. Forcing the transport block sizes to differ will enable laterdisambiguation of substream mapping in the event that both transportblocks 110 fail to decode successfully and must be re-transmitted later.

At block 420, the first and second transport blocks 110 are scheduledfor a first transmission interval. As with the previously describedmethod, a single re-transmission process identifier is assigned to thefirst transmission interval, at block 430. Likewise, schedulinginformation, including the re-transmission process identifier, istransmitted to the receiving node (e.g. a 3G mobile terminal) at block440. However, in this example, an explicit substream mapping bit is notsent as part of the scheduling information. Rather, in the event thatlater disambiguation is needed, i.e., in the event that are-transmission is required, the transport block size corresponding tothe re-transmitted transport block 110 is used to determine whichsubstream was used for the retransmission. Thus, the schedulinginformation transmitted at block 440 includes block size information foreach of the transmitted transport blocks 110. As noted earlier, thisblock size information may comprise explicit transport block size data,or it may be implicit in other transport format data included in thescheduling message.

At block 450, the Node B receives a NACK corresponding to one of thefirst and second transport blocks 110 transmitted during the firstinterval, indicating that the NACKed transport block 110 must bere-transmitted at a later interval. Accordingly, the primary orsecondary substream is selected for re-transmission of the NACKedtransport block, based on channel conditions, at block 460, and theNACKed transport block 110 is scheduled for re-transmission during asecond transmission interval (which may actually be several intervalsafter the first transmission interval), on the selected substream, atblock 470.

In the event that only one of the originally transmitted first andsecond transport blocks 110 was unsuccessfully decoded, and is thusscheduled for re-transmission in the second interval, an additionaltransport block, comprising new data, may be scheduled for transmissionalong with the re-transmitted transport block 110 during the secondtransmission interval. Thus, at block 480, a third transport block 110is selected, such that its transport block size differs from the NACKedtransport block 110. This third transport block 110 is scheduled for thesecond transmission interval at block 490.

Finally, at block 495, scheduling information corresponding to thesecond transmission interval is sent to the receiving node. Thisscheduling information includes the same process identifier as was sentwith the earlier scheduling information. In addition, this schedulinginformation includes transport block size information for each of thescheduled transport. The receiver may use the transport block sizeinformation to determine which of the substreams carries there-transmitted transport block, and which carries the new transportblock 110.

Those skilled in the art will appreciate that corresponding methods forprocessing the transmitted scheduling information are performed at thereceiving node, e.g., at the W-CDMA HSDPA mobile terminal. Exemplarymethods for receiver processing are thus illustrated in FIGS. 5 and 6,and briefly described below.

FIG. 5 illustrates an exemplary processing method in which thetransmitted scheduling information comprises an explicit substreammapping bit in addition to the retransmission process identifier. Atblock 510, scheduling information corresponding to a first transmissioninterval is received. This information may be received from, e.g., adownlink control channel such as the HSDPA HS-SCCH. The schedulinginformation includes a re-transmission identifier (e.g. a 3-bitidentifier), as well as a substream mapping bit. At block 520, first andsecond transport blocks 110 scheduled for the first transmissioninterval are received, on the primary and secondary substreams,respectively.

At block 530, in response to an unsuccessful decode of one of theblocks, a NACK message is sent to the transmitting node (e.g. the NodeB). Shortly afterwards, another scheduling message is received,comprising scheduling information for a second transmission intervalduring which the NACKed transport block 110 is scheduled to betransmitted. This scheduling information includes the same processidentifier as was received for the first transmission interval, as wellas a substream mapping bit. Because the receiver sent the earlier NACKmessage, and is thus “expecting” a retransmission, the appearance of thesame process identifier signals to the receiver that the re-transmittedblock is scheduled for the second transmission interval. Those skilledin the art will recognize that the appearance of the same processidentifier is not a perfectly reliable indicator of a re-transmission,as the Node B may have misinterpreted a NACK as an ACK and may actuallybe sending new data. An HSDPA receiver can detect this situation byexamining the re-transmission sequence number, or RSN, for eachsubstream; an RSN of zero indicates new data, while other valuesindicate redundancy versions in a pre-determined incremental redundancyscheme.

In any event, once the receiver has determined that a re-transmittedtransport block 110 is scheduled for the second interval, it must thendetermine whether the re-transmitted block 110 is scheduled for theprimary or secondary substream. The substream mapping bit correspondingto the second transmission interval may differ from the mapping bit sentfor the first interval. Accordingly, at block 550, the earlier substreammapping bit is compared to the newly-received mapping bit to determinewhether the re-transmitted transport block 110 is scheduled for the samesubstream as it was earlier received on, or whether it has beenscheduled for the other substream. In an exemplary embodiment, if themapping bits are identical for the first and second transmissionintervals, then the re-transmitted transport block 110 will betransmitted on the same substream as before. If the mapping bits differ,then the re-transmitted transport block 110 will appear on the oppositesubstream, compared to the original transmission.

At block 560 then, re-transmitted block data is retrieved from theappropriate substream during the second transmission interval. This datais combined, at block 570, with the corresponding block data from thefirst transmission interval using e.g., Chase combining or incrementalredundancy to improve the probability of successful decoding. At block580, a new transport block, which was scheduled for transmission alongwith the re-transmitted block, is also received from the secondtransmission interval.

In the exemplary method illustrated in FIG. 6, scheduling informationcorresponding to a first transmission interval is received, at block 610In this example, the scheduling information does not include an explicitsubstream mapping bit, but instead includes block size information.Again, the block size information may be explicit, or may be implicit intransport format information defining the modulation and coding schemesused for each substream during the interval.

At block 620, first and second transport blocks 110 transmitted duringthe first interval are received. As with the previous method, inresponse to a failed decode attempt for one of the blocks, a NACK issent to the transmitting node, at block 630. Subsequently, a secondscheduling message, corresponding to a second transmission interval, isreceived, the scheduling message comprising the same process identifierreceived for the first transmission interval. The second schedulingmessage further comprises block size information. In this embodiment,the receiver analyzes the block size information to determine whetherthe re-transmitted transport block 110 is scheduled for the primarysubstream or the secondary substream. Typically, the scheduling messagecomprises separate transport format data for each substream. From thistransport format data, the transport block size corresponding to eachsubstream may be derived. When the decoding of a transport block 110fails, the receiver saves information indicating which substream thefailed transport block 110 was received on. Thus, when the transportblock 110 is re-transmitted in a later interval, the receiver candistinguish the re-transmitted transport block 110 from a simultaneouslytransmitted transport block 110 by comparing transport block sizeinformation for each of the newly-received transport blocks 110 to thesaved information.

Once the receiver has determined which substream carries there-transmitted transport block, re-transmitted block data may bereceived during the second transmission interval, and combined withblock data saved from the first transmission interval, to decode there-transmitted block. This is shown at block 660.

An exemplary spatial multiplexing wireless communications system isillustrated in FIG. 7. Wireless communications system 700, which maycomprise a W-CDMA HSDPA system utilizing MIMO technology, comprises abase station 720, communicating with mobile terminal 750, using two ormore base station antennas 725 and two or more mobile terminal antennas755. Base station 720 comprises a transmitter subsystem 730, which isconfigured to perform fast packet scheduling, base-station receiver 740,and base-station controller 745. Exemplary mobile terminal 750 comprisesa receiver subsystem 760, a mobile transmitter section 770, and mobileterminal controller 775.

Transmitter subsystem 730 is configured to carry out one or more of themethods described herein, or variants thereof, for signaling schedulinginformation in a spatial multiplexing wireless communications system,such as wireless communications system 700. In particular, transmittersubsystem 730 may be configured to schedule first and second transportblocks 110 for simultaneous transmission during a first transmissioninterval on a primary and a secondary data substreams, respectively, andto transmit first scheduling information for the first transmissioninterval, the first scheduling information comprising a singlere-transmission process identifier as well as first disambiguation data.Transmitter subsystem 730 may be further configured to schedule thesecond transport block 110 for re-transmission during a secondtransmission interval, and to transmit second scheduling information forthe second transmission interval, the second scheduling informationcomprising the same re-transmission process identifier as well as seconddisambiguation data. As described in more detail above, the first andsecond disambiguation data indicate whether the re-transmission of thesecond transport block 110 is scheduled for the primary or secondarydata substream. Thus, in some embodiments, the first and seconddisambiguation data each comprise an explicit substream mapping bit, thevalues of which may be compared to determine whether the re-transmittedtransport block 110 is scheduled for the same or a differing substreamfrom which was used for the original transmission. In other embodiments,the substream mapping is implicit, and is derived from transport blocksize information included in the first and second schedulinginformation. In the latter embodiments in particular, the transmittersubsystem may be configured to ensure that the first and secondtransport blocks 110 have differing transport block sizes and may befurther configured to ensure that the re-transmitted transport block 110has a different transport block size than a third transport block 110transmitted during the second transmission interval along with there-transmitted block.

In some embodiments, re-transmission of a transport block 110 bytransmitter subsystem 730 is triggered by receipt of a NACK message,which may be received by base-station receiver 740 and relayed totransmitter subsystem 730 via base-station controller 745.

Receiver subsystem 750 is configured to carry out one or more of themethods described herein, or variants thereof, for processing schedulinginformation in a spatial multiplexing wireless communications system,such as wireless communications system 700. In particular, receiversubsystem 750 may be configured to receive first and second transportblocks 110 simultaneously transmitted during a first transmissioninterval on primary and secondary data substreams, after receivingscheduling information for the first transmission interval. The receivedscheduling information includes a single re-transmission processidentifier and first disambiguation data. In some embodiments, receiversubsystem 750 is configured to generate and send a negativeacknowledgement (NACK) to mobile controller 775, which relays the NACKto mobile transmitter 770 for transmission to base station 720. The NACKindicates that at least one of the first and second transport blocks 110transmitted during the first transmission interval was received witherrors. In any event, receiver subsystem 750 subsequently receivessecond scheduling information for a second transmission interval, thesecond scheduling information including the same re-transmission processidentifier along with second disambiguation data. Finally, receiversubsystem 750 is configured to use the first and second disambiguationdata to determine whether a re-transmitted transport block 110 isscheduled for re-transmission on the primary data substream or thesecondary data substream during the second transmission interval.

In some embodiments, the disambiguation data comprises a first andsecond substream mapping bit, corresponding to the first and secondtransmission intervals, and the receiver subsystem 750 is configured tocompare the first and second substream mapping bits to determine whetherthe re-transmitted transport block 110 is scheduled for re-transmissionon the primary data substream or the secondary data substream during thesecond transmission interval. In other embodiments, the disambiguationdata comprises transport block size information corresponding to there-transmitted transport block, and the receiver subsystem 750 isconfigured to determine whether the retransmitted transport block 110 isscheduled for re-transmission on the primary data substream or thesecondary data substream during the second transmission interval bydetermining whether the transport block size information corresponds tothe primary or secondary data substream during the second transmissioninterval.

In some embodiments, receiver subsystem 750 is configured to receive athird transport block 110 transmitted simultaneously with there-transmitted transport block 110 during the second transmissioninterval; in these embodiments the disambiguation data is used furtherto determine whether the third transport block 110 is scheduled for theprimary or secondary substream.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

What is claimed is:
 1. A method for signaling scheduling information ina spatial multiplexing wireless communications system, the methodcomprising: scheduling first and second transport blocks forsimultaneous transmission during a first transmission interval on firstand second data substreams, respectively; assigning a singlere-transmission process identifier to the first transmission interval;transmitting first scheduling information for the first transmissioninterval, the first scheduling information comprising there-transmission process identifier and first disambiguation data;scheduling the second transport block for re-transmission during asecond transmission interval; transmitting second scheduling informationfor the second transmission interval, the second scheduling informationcomprising the re-transmission process identifier and seconddisambiguation data; and wherein the first and second disambiguationdata indicate whether the re-transmission of the second transport blockis scheduled for the first or second data substream.